The present invention relates to a demand assignment time division multiple access (TDMA) communication system, and more specifically to maintenance control for switching between duplicated channels and giving a fault indication in the event of a channel failure.
In a TDMA communication system, each of a plurality of terminal stations establishes communication with another via a central station, and so the equipment of the central station is commonly shared by all the terminal stations. Thus, an equipment failure in the central station would seriously affect on the total traffic of the whole system. To avoid system interruption, the central station equipment is duplicated to instantly switch the communication path to a standby channel in the event of a trouble in the active channel. This requires the constant monitoring of the working conditions of the duplicated channels.
Hitherto, in a preassignment TDMA system, the whole system is monitored by effecting error check on the information bits of each time slot. If the error rate of each time slot exceeds beyond a preset value, the active channel is regarded as being faulty and the system is switched to the standby channel. However, the time-slot monitoring approach of the preassignment TDMA system would require a costly, complicated monitoring system if it is employed in a demand assignment TDMA system because the time slots would have to be monitored on an individual basis for fault location.